Effect of Rain Garden on
Ecological Network Improvement and Inland Flood Reduction
Akihide Ano
Key Words: City-Biodiversity, Climate Change, Inland Flood, Ecological Network, Rain Garden
1. Introduction: Rain Garden that contributes to Urban Biodiversity and adaptation to Climate Change
Attention for Urban Biodiversity is increasing because ecosystem services from urban nature can play an important
role to improve living environment or to help disaster reduction such as inland flooding which is increasing1). This
research deals with Rain Garden that not only contributes to urban biodiversity but also help environmentally friendly
rain water management. Rain garden is the shallow depression with native plants to gather and retain rain water from
impervious area2). It prevents rain water from running into the drainage by holding it and reduce the risk of flooding. It
also helps to improve local biodiversity by its plants. Rain garden is a popular effort in United States or European
countries. However, there is no rain garden in Japan. Therefore, the simulation has been done at Moriguchi city, Osaka
in order to verify the effect and installation potential.
2. The Effect of Rain Garden：Simulation of Effect of Rain Garden
Study area is between Yodo River and Tsurumi Green Park. First, extract permeable area. Second, search the site to
be able to apply the rain garden. Third, compare the ecological network situation between before and after the
application of rain garden by Papilio Xuthus. Finally, evaluate the effect of reducing runoff by measuring infiltration capacity.
2. The Effect of Rain Garden
The area of isolated area to Papilio Xuthus has become less than half by converting 2% of whole area like roadside and parking side into rain garden. In terms of reducing risk of inland flood, rain garden play subsidiary role to
disastrous downpour by itself, so it is essential to apply all kinds of other method. Meanwhile, when we don’t think
disaster reduction but daily rain water management, rain garden can help rain water to be able to go back into the soil.
The simulation revealed that rain garden can deal with comparatively soft and short time downpour like 10 mm/hour
such as evening shower in summer. Taking all results into consideration, rain garden can be of help to carry forward the
effort that makes Japanese city more nature harmonious place by managing rain water with caring ecosystem.
3. Citation
１）内水ハザードマップ作成の手引き（案）.2008. 国土交通省都市・地域整備局下水道部
